This invention relates to an aircraft angle of attack sensor and, more particularly, to a vane-type forward fuselage mounted sensor having an internal force relief feature.
Angle of attack sensors typically include an external drag profile which is supported by a rotary shaft. The sensor is mounted on the side of the airplane fuselage and measures local airstream angle with respect to the fuselage horizontal reference plane. In one such sensor (a Safe Flight angle of attack sensor, 1703 series, manufactured by Safe Flight Instrument Corporation, White Plains, N.Y.), a small, wedge-shaped vane on the end of a movable arm senses the airflow. The arm is free to rotate through an arc of 60.degree. and is counterbalanced so that the position of the arm is determined entirely by the airstream direction around the wedge-shaped vane. The arm pivot is attached through anti-backlash gearing to two rotary induction potentiometers (linear transformers) which generate an electrical output calibrated in terms of angle of attack. Such sensors are also equipped with anti-icing heaters.
The drag member, or vanes which are used in angle of attack sensors, protrude outwardly from the aircraft's fuselage and are therefore vulnerable to damage or breakage. Such sensors frequently include a stop mechanism to limit the rotation of the vane. If then, the vane is rotated against the stop, a relatively small force, such as a stream of water used in washing the aircraft, may be sufficient to damage the vane. In other cases, service personnel may attempt to use the vanes as a hand hold or foot rest and damage the sensor.
Eliminating the rotational stops would permit full rotation of the vane and thus reduce the likelihood of damaging the vane during the servicing of the aircraft. However, permitting full rotation of the vane would permit rotation between 90.degree. to 180.degree. and, if the vane were left in that position, would cause erroneous signals.
Accordingly, it is now believed that there is a significant market for an improved angle of attack sensor which incorporates an internal force relief feature and a mechanism for automatically returning the vane to its operative position after activation of the force relief feature. The improved angle of attack sensor should also be less susceptible to damage on the ground when compared to most vane-type angle of attack sensors, include electrical anti-icing elements, permit vane replacement from outside the aircraft without removing or recalibrating the sensor and resist vane breakage which might result in the broken vane being ingested by an engine. The improved angle of attack sensors must also be reliable in operation and produced at a competitive price.
It has now been found that an improved angle of attack sensor in accordance with the present invention has the aforementioned characteristics.